The present invention relates to a water cooler. More specifically, the present invention relates to a water chilling and storage apparatus for use in a water cooler which provides low copper concentrations in the water and other benefits.
Water supplied by water coolers, whether pressure coolers or bottle coolers, is receiving increasingly stricter scrutiny for public health and safety. In particular, the maximum allowable presence of certain metals, such as copper, in potable water has been lowered by public and private regulatory and governmental bodies such as the EPA and the National Sanitation Foundation (NSF), as further discussed below.
Water coolers may be generally divided into two types: pressure coolers and bottle coolers. Pressure coolers rely upon municipal pipe-supplied water under pressure (e.g., 45-90 psi), whereas bottle coolers rely upon gravity-fed water supplied from a bottle. Both types of water coolers typically employ a storage tank for holding chilled water of some predetermined volume (e.g., 0.2-0.5 gallons or more). When chilled water is required, it is thus immediately available.
With conventional water pressure coolers, water flows from a pressurized source through copper tubing typically wrapped around the outside of, and in heat exchange relation with, the water cooler storage tank. Alternatively, the water tubing may be wrapped around the inside surface of the storage tank, provided the diameter of the wrapped coil is carefully controlled so that after the coil is placed inside the tank, the coil is in sufficient heat-exchange contact with the inner wall of the storage vessel. With either design, the water within the copper tubing is first cooled by a refrigerant, such as freon. The refrigerant tubing may be wrapped around the outside of the storage tank, and beneath the copper (water) tubing, as shown in FIG. 9. Cooling of the water continues within the storage tank due to the adjacent refrigerant tubing.
Some copper storage tanks have been manufactured in a manner that requires the use of substantial seam weld lengths. One common example is shown in FIG. 10, which illustrates a three-part tank with two semi-spherical dome-like portions welded to a cylindrical portion. Each seam line shown in FIG. 10 is a potential source of leakage, and is also susceptible to corrosion due to the presence of degraded material in the weld seam. Brazed holes are typically provided in copper storage tanks to accept the copper tubing carrying the water. The brazed areas around these tubing openings in the tank are also potential sources of leakage and corrosion.
Water cooler storage tanks of the design shown in FIG. 10 have also been available in stainless steel. Spun copper tanks, as shown in FIG. 9, have also been available, eliminating weld seams but still requiring brazed water and refrigerant conduit holes.
Also, certain low capacity storage tanks have been made of seam-welded stainless steel and have not employed wrapped copper water tubing at all.
In addition to the problems referenced above with the use of an all-metal storage tank for water coolers, the emission of copper into potable water supplies is also regulated. To increase heat transfer efficiency, water cooler storage tanks have generally been made of copper. Copper is an excellent conductor of heat, easy to work and form, and relatively simple to solder or braze. The use of copper in plumbing systems for the supply of potable water is widespread. ANSI (American National Standard Institute)/NSF 61 is currently a voluntary standard that regulates the presence of certain contaminants in drinking water systems. ANSI/NSF 61 ("NSF 61") covers all materials that come in contact with potable water supplies. The majority of components used in the construction of water coolers are in compliance with NSF 61 or are relatively easily changed to be in compliance. However, shortly after NSF 61 was promulgated, it became clear through testing that the copper water storage tank and related heat exchanger components (i.e., incoming and wrapped/heat exchange water tubing) are the principal components requiring modification to meet the maximum copper emission level of NSF 61. The level emitted by conventional such components was typically 3-4 times the maximum allowable level.
NSF 61 limits copper emissions to a maximum contaminant level of 130 parts-per-billion (ppb), which is at 10% of the EPA-allowed level. NSF 61 is a durational test with numerous specific requirements; it also employs a normalization factor of one liter, so that if a storage tank has a capacity of one-half liter, a dilution factor of 100% is used, meaning that 260 ppb of copper emissions is allowed for a one-half liter storage tank, since one-half liter of pure water will then be added to the test sample. However, if the storage tank has a capacity of one liter or more, then copper emissions must be less than or equal to 130 ppb. 36 states have now adopted NSF 61, and enforcement of this standard is expected soon. No currently available water coolers employing storage tanks with wrapped copper water tubing meet this standard.
A second style of known water cooler storage tank design is a "tube-on-tube" design. This incorporates a large-diameter coiled water tube (e.g., 0.75" diameter) wound side-by-side with a refrigerant tube (e.g., 0.25"-0.35" diameter). Here, the large water tubing doubles as the "storage tank". Using currently available copper water tubing, however, NSF 61 cannot be met with this tube-on-tube design, either. Further, stainless steel is difficult to bend into the forms required for this design.
In circumventing the NSF 61 copper emissions problem, feedback from copper suppliers was not helpful. Specifically, no known copper suppliers provide NSF-61 compliant tubing. Further, queried suppliers were not aware of any treatments or selection processes that could be performed on copper tubing to reduce copper emission levels. Instead, the copper industry lobbied NSF in an attempt to change or remove the NSF 61 limit for copper.
Plating operations were also attempted to obtain NSF 61 compliance. Nickel plating of a copper storage tank, for example, was tested. However, while this was successful in limiting copper emissions in the tank, NSF 61 limits for nickel were exceeded. Further, plating does not address copper contact levels for water coils wrapped around the storage tank.
Accordingly, it is an object of the present invention to provide a water cooler capable of limiting copper emissions to less than 130 ppb so that NSF 61 may be complied with.
It is another object of the present invention to provide a process for treating and/or selecting copper tubing which provides substantially decreased copper emissions.
It is a further object to provide a process for the manufacture of copper and copper alloy components and fittings for use in contact with potable water which provides substantially decreased copper emissions.
It is yet another object to provide a non-copper water cooler storage tank.
It is still another object to provide a water cooler storage tank with decreased leakage and corrosion characteristics.
These and other objects and advantages of the present invention will become apparent to those of ordinary skill in the art from reading the following description of the preferred embodiments, drawing and appended claims.